Semiconductor lasers are commonly used as optical signal generators in fiber optic communications systems. The optical signals generated by a semiconductor laser are transmitted through an optical waveguide, such as an optical fiber, to their destination. An important aspect of an optoelectronic component employing a semiconductor laser is the coupling of the output light from the laser to an optical fiber. Typically, a semiconductor laser is packaged with a lens in an optical subassembly (OSA) to focus the output light from the laser into an exposed end of an optical fiber to ensure good coupling efficiency. Thus, the semiconductor laser and the lens must be properly aligned so that the output light from the laser is effectively transmitted to the optical fiber.
There are two distinct types of semiconductor lasers used in fiber optic communications systems. The first type of semiconductor lasers includes edge-emitting lasers, such as Fabry-Perot (FP), Distributed Feedback (DFB) lasers and Distributed Bragg Reflector (DBR) lasers. The other type of semiconductor lasers includes vertical-emitting lasers, such as Vertical Cavity Surface Emitting Lasers (VCSELs). The edge-emitting and vertical-emitting lasers are usually packaged so that the output light from an edge-emitting laser or a vertical-emitting laser propagates along a straight optical path from the laser through a lens and to the fiber (or optical waveguide). Thus, OSAs with vertical-emitting lasers cannot be readily interchanged with OSAs with edge-emitting lasers since the propagating direction of the output light depends on the type of lasers employed in the OSAs. However, OSAs with edge-emitting lasers have been developed that can turn the output light from the original horizontal direction to the vertical direction, which allows these OSAs to be interchanged with OSAs with vertical-emitting lasers.
A conventional OSA with an edge-emitting laser that can transmit the output light in the vertical direction includes a 45-degree mirror structure and a lens. The edge-emitting laser and the mirror are mounted on a substrate such that the output light from the laser is reflected off the reflective surface of the mirror structure. Thus, the output light from the laser is redirected from the original horizontal direction to the vertical direction. The lens is attached to the mirror structure to focus the redirected output light propagating in the direction of an optical fiber.
A concern with conventional OSAs with edge-emitting lasers that can vertically transmit output light is that precise alignment of various elements of the OSAs, such as the laser, the mirror structure and the lens, is difficult to achieve for proper coupling of the laser to an optical fiber.
In view of this concern, there is a need for an OSA with an edge-emitting laser that reduces the difficulty of precisely aligning the various components of the OSA.